There has been proposed a dried food manufacturing apparatus, for example, such as that disclosed in Japanese Patent Public Disclosure No. 120973/1985. This apparatus is so constructed that foods to be dried are introduced into a chamber of reduced pressure and dried by an extreme infrared radiation heating apparatus. However, since a vacuum pump is not arranged in each of an inlet chamber, a drying chamber and an outlet chamber, it is impossible to continuously and effectively carry out the reduced pressure drying treatment of foods.
In addition, the above mentioned apparatus is so constructed that the water vapor derived from foods is introduced into the vacuum pump by a ventilating fan mounted in the heating apparatus at an upper portion thereof in order to expel the water vapor from the drying chamber. However, since the ventilating fan does not operate when the pressure within the drying chamber is reduced below 50 torr, the vaporizing rate of water contained in foods to be dried is reduced and therefore the drying effect is also lowered.
There are other known dried food manufacturing apparatuses, for example, such as disclosed in Japanese Patent Public Disclosure Nos. 31659/1984, 156272/1984 and 156273/1984. However, all of these apparatus esare formed as batch types and therefore it is impossible to carry out the continuous drying treatment of foods, and they adopt a single-stage pressure reduction system in which a vacuum chamber (a reservoir tank) is connected to the drying chamber. Accordingly, it is impossible to carry out the reduced pressure heating treatment in the drying chamber during evacuation of the vacuum chamber.
It is an object of the present invention to provide a reduced pressure swelling and drying apparatus which is able to continuously carry out the reduced pressure drying of foods and to eliminate the above mentioned problems of the prior art.
It is another object of the present invention to provide a reduced pressure swelling and drying apparatus which is able to effectively carry out the evacuation of the reduced pressure drying chamber.
It is still another object of the present invention to provide a reduced pressure swelling and drying apparatus which is able to simply and effectively carry out the drying of foods in the drying chamber.